[TheForge] Quenching mild steel - Hochewa ?

Wed Sep 3 20:10:00 2003

The book (engineer's bible) Steel Structures: Design and Behavior Salmon &
Johnson says A36 has a maximum of  .25-.29% carbon.  They also categorize
mild steel as having an upper limit of 0.29% carbon (then you get into
"medium carbon" steels).

I've heard from a few engineers that A36 can have pretty high carbon content
due to the recycling of steels such as car axle stock.  Apparently some
engineers got concerned that structures designed for a certain amount of
ductility at failure (i.e. earthquake) would not behave as safely as
planned.  Maybe the actual case is that the carbon is in spec. but other
alloying elements are present in a combination that makes harder steel.

From personal experience I can say that I used to make tons of hooks out of
1/4" cold rolled mild steel (probably 1018), and even that was an issue to
drill a small hole through if quenched with any color.

Ed

----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 03, 2003 6:13 PM
Subject: Re: [TheForge] Quenching mild steel - Hochewa ?

> To All,
> Do y'all know that I have a sister named Pandora?
>
> You can form martensite with 1010 steel.  There is not a high percentage
of
> it in the work and it isn't very hard.
>
> Martensite or super-cooled austenite can only form if you clear the
pearlite
> nose on the TTT curve.  It is just the physics of the system.
>
> The pearlite nose is at about 1200*F, more or less.  The more effective
the
> quench is between the austentizing temperature and 1200*F the better the
> chances are that you will clear it.
>
> Alloys tend to push the curve to the right.  More alloy, more time, slower
> quench, deeper the hardening.
>
> Carbon has the single most potent effect on the hardness of martensite and
> the effect levels out about 0.6% carbon.  After that it adds more to wear
> resistance than hardness.
>
> There are no reports in any journals to which I have access that describes
a
> new phase that is the result of using "super-quench".
>
> The maximum allowable carbon in A-36 is about 0.35%.  Also 1.25% or so of
> manganese is allowed and manganese is a potent hardenability agent.  It is
no
> small wonder that A-36 can be hardened if it is austenitized and quenched
> properly (or improperly).   4140 is pretty hard when fully hardened.  What
differnce
> does 0.05% carbon make?
>
> For plain carbon steels, A-36 included, it is ok to cool them any which
way
> you please provided that you realize that you may have just hardened it
enough
> that a blow from a hammer could crack it or that it may be a little hard
on
> drill bits.  If you "quench" the work, take the time to reheat it before
any
> other operations.
>
> For plain carbon steels, black is ok to be quenched in clean, fresh water
> without much happening.  For any tool steel that does not have a W in
front of a
> number, water may not be a good choice.
>
> Regards,
>
> Hochewa
>
>
>
> In a message dated 9/3/2003 12:31:16 PM Eastern Standard Time,
> [email protected] writes:
> This is one for the "Rt. Rev. Hochewa of the Church of Orthodox
Metallurgy"
>
> "There is nothing SUPER or magic about "super quench" it is just a fast
> quench made to be similar to quenching in a solution of NaOH without the
> high risk to person of the caustic."  I for one, wish Rob had called it
> something besides "super".  I am not saying it isn't a good quench
media --
> just that there is no magic -- it is just fast, like NaOH but much safer.
>
> By the way are you asking about 1018 or A36 hot rolled?
>
>
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